IP Multi-Media Subsystem (IMS) defined by the 3GPP and 3GPP2 standards open the door to a whole range of new multimedia services, such as Voice over IP (VoIP) and IPTV. The IMS service architecture enables to combine multimedia services of various types.
One type of services may enable viewers at home to participate real-time in a live TV show using e.g. a webcam at home. The multimedia streams generated by the webcam are transported from the home-located user over an IP network to the TV studio using the Real-time Transport Protocol (RTP). In an IMS based architecture such multimedia streaming sessions between clients are set up using the Session Initiation Protocol (SIP), whereas the Real Time Streaming Protocol (RTSP) is typically used for streaming multimedia content from a server to a client.
Systems that provide an interface between SIP and RTSP domains, usually referred to as SIP-RTSP gateways, are known in the art. Within ETSI TISPAN Standardization (WI2048, TS 182 027) an architecture is proposed in which a terminal, comprised in a device such as for example a set-top box, a personal computer, a personal digital assistant (PDA) or a mobile telephone with multi-media capabilities, uses SIP to set up a multimedia session with a selected content provider. After establishment of the session, RTSP is used to select, retrieve and control the streamed content. Further, the University of Colombia (Kundan Singh and Henning Schulzrinne, “Unified Messaging using SIP and RTSP”, IP Telecom Services Workshop, September 2000, Atlanta, Ga., US) has developed a SIP-RTSP Gateway for multimedia unified messaging.
These systems use SIP and RTSP clients at the user side and SIP clients and RTSP servers in the network, thereby enabling a user to initiate the set up multimedia session in which multimedia content is streamed from the RTSP servers to the user.
Another gateway system that may be used to stream multimedia between different protocol domains is described in TAKEI K ET AL “Design of gateway system between different signaling protocols of the multimedia session on the internet” INFORMATION NETWORKING, 2001. PROCEEDINGS. 15TH INTERNATIONAL CONFERENCE ON 31 January-2 February, PISCATAWAY, NJ, USA, IEEE, 2001, PAGES 297-302, ISBN: 0-7695-0951-7/01. This system is used to interwork the SIP and the H323 protocol domains. Both protocols are peer-to-peer type protocols and allow for bidirectional set-up/initiation of sessions.
One problem related to these known systems is that they do not provide all the functionality needed for the above mentioned services, which require the user to initiate the set up a multimedia session such that user-generated content is streamed from the user (the transmitting-end) to the studio (the receiving-end), whereby the studio may want to control the stream of user generated content. A known protocol for controlling a stream is RTSP, whereby the receiving-end, with RTSP client functionality, may be able to pause, or forward or backward a stream, or play a stream at a different speed. If the transmitting-end on the other hand is only capable of using the SIP protocol for setting up and maintaining the multimedia streaming session, the mentioned services cannot be realized with the known prior art systems, since the SIP protocol does not provide the means for controlling a stream in the way that for instance the RTSP protocol is capable of.
Another problem related to the streaming of multimedia, that may arise with prior art systems, is that when the receiving-end is only equipped with client functionality of a client-server type of protocol for receiving multimedia, it may only be capable of initiating a multimedia session. If the transmitting-end, using for example a peer-to-peer type of protocol, such as the SIP protocol, wants to initiate a multimedia streaming session, the receiving-end is not capable to respond to such an invitation. Prior-art systems, such as the known SIP-RTSP gateways and the known SIP-H323 gateways do not provide a solution for this problem.
A variety of additional problems may arise with prior art systems, when the user generated multimedia has to be streamed to a multiple of receiving-ends. These receiving-ends may all have different capabilities or preferences when it comes to receiving a multimedia stream. One receiving-end may want to receive a live stream, whereas the other may want to be able to control the stream as described above. Additionally these preferences and capabilities, as well as the network addresses of the receiving-ends, may not be known to the transmitting-end.